Literal.isDifferent can return wrong result for numeric literals

[tobias-hammerschmidt]

Due to the datatype simplification for numbers in pellet (see com.clarkparsia.pellet.datatypes.OWLRealUtils.getCanonicalObject(Number)) the method isDifferent in class org.mindswap.pellet.Literal might return wrong results for numeric literals. I've observed this behavior for 2 literals where one literal represented the value 0 using the java class Byte and one literal representing the value 200 using the java class Short. Due to the different classes the check within isDifferent always returns false:

    @Override
    public boolean isDifferent(Node node) {
        if( super.isDifferent( node ) ) {
            return true;
        }

        Literal literal = (Literal) node;
        if( hasValue && literal.hasValue ) {
            return value.getClass().equals( literal.value.getClass() )
                        && !value.equals( literal.value );
        }

        return false;
    }

so 0 and 200 are not threated as different and are even considered for merging.